The disclosure of Japanese Patent Application No. 2000-136046 filed on May 9, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a control apparatus and a control method of a direct injection type internal combustion engine in which fuel delivered from a fuel pump is directly injected into a combustion chamber from a fuel injection valve and the thus-formed mixture is ignited by an ignition plug. In particular, the invention relates to a direct injection type internal combustion engine control apparatus that automatically stops a direct injection type internal combustion engine if during operation of the internal combustion engine, the operating state of the engine meets an automatic stop condition, and that automatically starts operation of the engine if an automatic start condition is met.
2. Description of Related Art
A conventional direct injection type internal combustion engine is known which realizes lean burn when the engine is in a low load state, for example, during idling or the like, and thereby achieves both high output and reduced fuel consumption and also reduces emissions of carbon dioxide and the like (Japanese Patent Application Laid-Open No. 10-299543). In order to ensure that the mixture will be ignited without fail during lean burn, such a direct injection type internal combustion engine performs stratified charge combustion in which fuel is injected during the compression stroke to provide a fuel-rich mixture stratified around the ignition plug before being ignited to burn. In a case where the combustion is to be performed at a stoichiometric air-fuel ratio, the engine performs uniform combustion in which fuel is injected during the intake stroke to produce a state in which fuel is uniformly dispersed in the entire combustion chamber before being burned.
An automatic stop/start apparatus for an automotive internal combustion engine, that is, a generally-termed economy running system, is known which, for the purpose of improving fuel economy or the like, automatically stops the internal combustion engine at the time of a stop of the motor vehicle at an intersection or the like, and then automatically starts the engine by turning the starter upon an operation for starting the vehicle so that the vehicle can be pulled off (Japanese Patent Application Laid-Open No. HEI 10-47104).
Therefore, by combining this automatic stop/start apparatus with the above-described direct injection type internal combustion engine, a further fuel economy improvement can be expected.
For fuel injection during the compression stroke of a direct injection type internal combustion engine, fuel needs to be injected into a high-pressure combustion chamber. Therefore, a typical direct injection type internal combustion engine employs a high-pressure fuel pump to highly pressurize fuel and deliver high-pressure fuel toward the fuel injection valve side.
However, when such a direct injection type internal combustion engine is automatically stopped by the automatic stop/start apparatus, the high-pressure fuel pump also stops. Therefore, during the automatic stop, high-pressure fuel is not supplied to the fuel injection valve side. Even though the fuel injection valve side, including the fuel piping, is tightly closed, fuel gradually leaks. Therefore, during the automatic stop, the accumulated fuel pressure drops.
After that, at the time of an automatic start, the driving of the fuel pump is started. However, if the fuel pressure is insufficient for the compression-stroke fuel injection due to a fuel pressure decrease occurring during the automatic stop, it is inevitable to perform uniform combustion in which fuel is injected during the intake stroke during which good injection is possible even at low fuel injection pressure, until a sufficient fuel pressure is recovered. Therefore, even if the operating state of the engine other than the fuel pressure allows stratified charge combustion upon automatic start, the uniform combustion must be performed. Hence, the improvement in fuel economy and the like may become insufficient.
It is an object of the invention to provide a direct injection type internal combustion engine control apparatus capable of maintaining a sufficient fuel pressure for the compression-stroke fuel injection for a long time even after the internal combustion engine has been stopped by an automatic stop function, and capable of increasing the frequency of performing the compression-stroke injection after the engine is automatically started. Operation and advantages obtained by the invention will be described.
A control apparatus of. a direct injection type internal combustion engine in which an air-fuel mixture formed by injecting a fuel delivered from a fuel pump, directly from a fuel injection valve into a combustion chamber, is ignited by an ignition plug, the control apparatus is provided with an automatic stop permitting unit that permits an automatic stop of the internal combustion engine if during an operation of the internal combustion engine, an operating state of the internal combustion engine meets an automatic stop condition, an automatic start permitting unit that permits an automatic start of the internal combustion engine if the operating state of the internal combustion engine meets an automatic start condition, and a fuel pressure raising unit that raises a fuel pressure on a fuel injection valve side during a first period of time_prior to the automatic stop permitted by the automatic stop permitting unit.
The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side immediately prior. to the automatic stop. Therefore, after the delivery of high-pressure fuel from the fuel pump stops upon the automatic stop of the direct injection type internal combustion engine, the fuel pressure starts to gradually decrease from a higher fuel pressure, in comparison with the conventional art in which the engine is stopped with an ordinary fuel pressure state. As a result, a long time of engine stop is allowed before the fuel pressure decreases to a pressure that makes it impossible to perform appropriate fuel injection into the combustion chamber during the compression stroke.
Therefore, the possibility that a fuel pressure sufficient for the compression-stroke fuel injection will be maintained immediately after a subsequent automatic start is increased. If such a fuel pressure is maintained, the stratified charge combustion can be accomplished by performing the compression-stroke injection immediately after the subsequent automatic start provided that the internal combustion engine is in an operating state that allows the stratified charge combustion. Thus, the frequency of performing the compression-stroke injection following an automatic start can be increased, and sufficient improvements in fuel economy and the like can be achieved.
The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side during the first period of time prior to the automatic stop by adjusting an amount of the fuel delivered from the fuel pump to a maximum.
Thus, by maximizing the amount of delivery from the fuel pump, the fuel pressure can be quickly brought to a sufficiently high pressure state. As a result, the frequency of performing the compression-stroke injection following an automatic start is further increased, and a fuel economy improvement and the like will become more effective.
The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. During the first period of time prior to the automatic stop, the fuel pressure raising unit raises the fuel pressure on the fuel injection valve side so as to temporarily open the relief valve by adjusting the amount of the fuel delivered from the fuel. pump to the maximum.
During the pressure raise continuation duration immediately prior to the automatic stop, the fuel pressure raising unit raises the fuel pressure by adjusting the amount of delivery from the fuel pump to the maximum, so that the relief valve is temporarily opened. This may open the relief valve, which is hardly ever opened during normal operation.
Therefore, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the locking or fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.
Furthermore, by setting a long pressure raise continuation duration so as to deliver a large amount of high-pressure fuel toward the fuel injection valve side and to discharge fuel via the relief valve, a reduced fuel temperature on the fuel injection valve side can be achieved immediately prior to the automatic stop. Therefore, it is possible to maintain a sufficiently high fuel pressure achieved by thermal expansion caused by increases in the fuel temperature during the automatic stop of the engine. Consequently, the frequency of performing the compression-stroke injection following an automatic stop can be further increased, and improvements in fuel economy and the like can be more effectively achieved.
The control apparatus is further provided with a fuel pressure control unit that adjusts the fuel pressure on the fuel injection valve side to a target fuel pressure that is set in accordance with the operating state of the internal combustion engine by adjusting an amount of the fuel delivered from the fuel pump. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side prior to the automatic stop by correcting the target fuel pressure to a higher level.
If the fuel pressure control unit adjusts the fuel pressure to a target fuel pressure in accordance with the operating state of the internal combustion engine by adjusting the amount of delivery from the fuel pump, the fuel pressure raising unit is able to raise the fuel pressure by correcting the target fuel pressure set by the fuel pressure control unit in accordance with the operating state of the internal combustion engine to an increase side immediately prior to the automatic stop.
Therefore, immediately prior to the automatic stop, the control apparatus realizes a high fuel pressure that is higher than a usual fuel pressure adjusted by the fuel pressure control unit. As a result, a longer-than-usual time of engine stop is allowed before the fuel pressure decreases to a pressure that makes it impossible to perform fuel injection into the combustion engine during the compression-stroke injection.
Therefore, the possibility of performance of the compression-stroke injection immediately following a subsequent automatic start is increased, and the frequency of performing the compression-stroke injection is increased. Thus, sufficient improvements in fuel economy and the like can be achieved.
The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side to at least the predetermined valve opening pressure of the relief valve prior to the automatic stop.
The fuel pressure raising unit raises the fuel pressure to at least the predetermined valve opening pressure of the relief valve provided on the fuel injection valve side, immediately prior to the automatic stop. This provides an occasion of opening the relief valve, which is hardly ever opened during normal operation.
Therefore, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.
The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side to at least the predetermined valve opening pressure of the relief valve prior to the automatic stop.
Thus, during the pressure raise continuation duration after the fuel pressure raising means raises the fuel pressure to or above the set valve opening pressure of the relief valve, the fuel pressure raising means further continues the process of raising the fuel pressure to or above the predetermined valve opening pressure of the relief valve. Therefore, during the pressure raise continuation duration just prior to the automatic stop, the relief valve is continuously or repeatedly opened, so that a large amount of fuel can be delivered toward the fuel injection valve side and a large amount of fuel can be discharged via the relief valve. Hence, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.
Furthermore, by setting the pressure raise continuation duration, it becomes possible to deliver a large amount of fuel toward the fuel injection valve side and discharge a large amount of fuel via the relief valve. Thus, a reduced fuel temperature on the fuel injection valve side can be achieved immediately before the automatic stop. Hence, it becomes possible to maintain a sufficiently high fuel pressure achieved by thermal expansion caused by increases in the fuel temperature during the automatic stop of the engine. Consequently, the frequency of performing the compression-stroke injection following an automatic stop can be further increased, and improvements in fuel economy and the like can be more effectively achieved.